A femto base station is basically a low cost and low power base station (BS) transceiver which is installed indoors (e.g., in a home or office) and connected to the Internet via cable, DSL, on-premise fiber optic link, or a similar IP backhaul technology. This connection is used to integrate the femto base station with the WAN wireless operator's core network.
A femto base station serves a geographic area known as a femto cell over a single carrier or channel. A femto cell typically covers a smaller geographic area or subscriber constituency than a conventional macro cell. For example, femto base stations typically provide radio coverage in geographical areas such as one or more buildings or homes, whereas conventional macro base stations provide radio coverage in larger areas such as an entire cities or towns. The function of femto cells is similar to that of a Wireless LAN (Local Area Network). It provides the operators a low cost solution for coverage extension and for offloading users from the cellular network.
A femto base station is typically installed by an end user rather than a network operator. When a femto base station is installed to enhance local coverage, for example, in a home, the femto base station should be dedicated to the home because the wireless resources are provided, installed and/or paid for by the end user. In such cases, only mobile stations associated with the home or authorized by the end user should be allowed to access the femto base station.
Conventionally, a radio access network (RAN) may prioritize user access to wireless resources within a cell (femto or macro) using initial configuration parameters and sector-parameters, which will be described in more detail below. However, no mechanism for preventing unauthorized users from tying up wireless resources provided by the femto cells. Consequently, an end user may be denied access in view of the femto base station being preoccupied with serving unauthorized users.
A mobile station receives the above-mentioned initial configuration parameters from a radio access network (RAN) during session configuration (e.g., at power up). Session configuration is typically triggered in response to, for example, a universal access terminal identification (UATI) request from the mobile station. The initial configuration parameters are sent via a traffic channel.
In the current 3GPP2 CDMA2000 EVDO standard “cdma2000 High Rate Packet Data Air Interface Specification,” 3GPP2 C.S0024-B, Ver. 2.0 (March 2007), the initial configuration parameters may include a class mask along with other parameters. As is well-known, a class mask is indicative of a priority class of the mobile station. Methods for assigning class masks are well-known in the art, and thus, a detailed discussion will be omitted for the sake of brevity. After completing session configuration, the mobile station may stay in a connected state or enter an idle state.
After entering an idle state, the mobile station periodically wakes up and receives broadcast overhead messages such as a sector-parameters message on the broadcast control channel. In the above-described current 3GPP2 CDMA2000 EVDO standard, sector-parameters include, for example, a channel mask, a trigger code and one or more color codes. As is well-known, channel masks are assigned by and maintained in the RAN. Channel masks indicate channels used for communication within a particular cell. Each channel may be associated with a particular priority class of users within the RAN.
Upon receiving a channel mask in a sector-parameters message, the mobile station performs a hashing calculation using its assigned class mask to determine which channels the mobile station is authorized to use. The mobile station then hashes on (or randomly selects) a channel through which to access the wireless resources provided by the newly entered cell. The access hashing mechanism supported in current standards only takes effect when there is more than one carrier (channel) supported by a particular base station. If only one carrier is supported by the base station, any mobile of any priority class may gain access to the carrier.
As is well-known, different cells may broadcast different channel masks. Consequently, when the mobile station moves from a femto cell to a macro cell or vice versa, the channel mask received by the mobile station changes. Upon receiving a new or different channel mask, the mobile station performs another hashing calculation to determine which channels the mobile station is authorized to hash on and use. The mobile station then hashes on an authorized channel through which to access the wireless resources provided the newly entered cell.
In a more particular example, assume a mobile station entering a macro cell is a low priority user and there exists five candidate channels allocated to the macro cell. Three of the candidate channels are associated with the low priority class of the mobile station, and two of the candidate channels are associated with a higher priority class. By performing the well-known hashing calculation using its assigned class mask and the channel masks broadcast by the cell, the mobile station determines that the three low priority channels are the only channels on which the mobile station is entitled to access. The mobile station then hashes on (or randomly selects) one of the three low priority channels through which to access the wireless network.
Using this conventional mechanism in a femto cell with a single carrier, however, users are not entirely denied access because only a single carrier exists. Thus, users entitled to use of wireless resources in the femto cell may be denied in favor of users not entitled to use of the resources.